Calutron electric lens



H. w. B. SKINNER 2,668,242 CALUTRON ELECTRIC LENS Feb. 2, 1954 Filed Nov. 25. 1947 INVENTOR. H. W5. SK/NNER MAGNET/C HELD Patented Feb. 2, 1954 UNITED STATES PATENT OFFICE CALUTRON ELECTRIC LENS Herbert W. B. Skinner, Harwell, England Application November 25, 1947, Serial No. 787,878

4 Claims. 1

This invention relates to the focusing of divergent ion beams and more particularly relates to improved electrostatic focusing means for increasing the sharpness of the foci of divergent arcuate ion beams in the electromagnetic separation of isotopes.

In the operation of devices which employ electromagnetic means for separating isotopes the high current ion beams generally employed are ion beams which have a virtual line source parallel to the magnetic field, and in addition have considerable divergences in a plane transverse to said magnetic field. Furthermore, whereas certain ions such as for example U and U have a theoretical foci separation at the 180 position of over two inches for ion beam radii of about 50 inches, it has been found that when employing no other focusing means than that of the uniform magnetic field, the beams will have an actual separation of less than an inch and with the degree of sharpness of focus thereby obtainable will therefore, overlap in the region of their maximum separation. Thus in order to obtain a separation of the ion beams which will approach the theoretical foci separation of about two inches, it is necessary to provide an arrangement which will divert them from their normal arcuate paths and into sharp foci in the region of their maximum separation.

In the copending application of H. W. B. Skinner, Serial No. 787,877, filed November 25, 1947, there is described an electrostatic focusing arrangement consisting of four parallel spaced substantially identical overlying decks, each deck being comprised of a shield shaped central plate electrode nested within similarly curved and successively nested strip electrodes. Those electrodes in successive decks which are identical and their edges being in a common magnetic projection are electrically connected to a source of potential with the exception of the outermost strip electrodes which are grounded to the calutron tank in which the electrostatic lens is mounted. Working inwardly from the outermost strip electrodes, successively adjacent sets of electrically connected electrodes are, each in turn, connected to a source of potential of value and sign determined by design considerations. The series of curvilinear edges of adjacent nested electrodes set up, in accordance with the respective potentials applied to these electrodes, a series of nested equipotential surfaces similarly curved; said equipotential surfaces being disposed transversely to the path of the divergent arcuateion beam. The relative strength and configuration of the equipotential surfaces encountered by the ion beam divert the component ions thereof through'a series of small angular deflections, thereby directing ions having equal mass to charge ratios to a common focus.

The present invention concerns an electric lens similar in certain respects to the electric lens described in the foregoing, however, present improvements are incorporated to further reduce the ion absorption of the lens structure by providing vertical focusing of the ion beam at the leading focusing elements so that fewer ions in their arcuate traverse will impinge the trailing focusing elements.

It is therefore an object of the invention to improve the electromagnetic separation of isotopes by increasing the sharpness of foci of divergent arcuate ion beams.

It is a further object of this invention to improve the sharpness of foci of divergent arcuate ion beams in the electromagnetic separation of isotopes beyond the sharpness which can be obtained through the effect of the magnetic field alone.

It is a further object of this invention to increase the sharpness of foci of divergent arcuate ion beams by imposing equipotential surfaces in the path of said ion beams.

A further object of this invention is to minimize the ion absorption of the electrostatic lens system by use of leading and trailing electrodes wherein the leading electrodes produce a certain amount of vertical focusing of the ion beam, the trailing electrodes being planarly offset relative to the leading electrodes thereby being positioned in a region of the ion beam having minimum ion density.

Other objects and advantages of the invention will be apparent in the following description and claims considered together with the accompanying drawings in which:

Figure 1 is a plan view of the calutron tank with the top plate removed showing the electrostatic lens positioned therein with relation to the ion transmitter, the divergent arcuate ion beam, and the ion receiver.

Fig. 2 is a partial front indicated by section line 22 in Fig. 1 showing the electrostatic lens assembly mounted on the bottom plate of the calutron tank bymeans of insulators.

elevational section as lens 'I l,

.ipotential surfaces field strengths of these surfaces, ,those ions havpresent invention comprising multiple.strip,..electrodes arrangedm receiver [4 being mounted on the front wall I2b of tank l2. The tank I2 is disposed between the pole faces of a magnet, the magnetic field thereof passing transversely through the top wall IM and the bottom wall I20. The direction of said field is indicated by arrows as shown in Fig. 2. The electric lens assembly H (see Fig. 2) is mounted on the bottom wall I20 of the calutron tank [2 by means of electrical insulators I6 which in turn attach to conducting ands importing 11D- rights H. The lens H consists f upper and lower substantially identical shield shaped plate electrodes I8 which are normal to the magnetic field of the calutron and which have disposed between them two sets of parallel strip electrodes l9 and 20 having their outer edges pf ithe same configuration as, and parallel to, the respective peripheral edges of the electrodesda. 'Moreover, the electrodes 19 are staggered along ithepmagnetic field with respect tothe electrodes 20. Auxiliary sets of .parallel strip electrodes .22 and 13 are positioned adjacent to the outer edges .oi the electrodes [9 and 2.0, the electrode 2?- bcing co planar with the electrodes 19 and the electrodes 23 being coplanar with the electrodes T26. EIhe adjacent edges oflthe electrodes 1,9 andZZ. and the electrodes 20 andl23,irespectively, define the electrostatic retracting regions of the electric lens H.

Considering now the electrical vcopnections of there are three components insulated from one another, comprising: electrodes "22 p interconnected by their conducting uprights 1" .plate electrodes 18 electrodes .119 sand .29 linterconnected by their respective conducting .11! rights l1. and i'electrodes 113 ,also interconnected by conducting uprights 11 1. "The three.components describedarecbnmctedlto ,difierient sources .of electricalpotential, .each' potentialjzli-being of proper value and signaspredetermined bydesign considerations.

"In operation, the jdivergentarcuatelionbeam inpassing throughthe region encompassejdhy the electrostatic lens .encountersla series of equi- .potential surfaces ,substantiallyof .a configuration defined-by the .magneticprojection of the edges of the various electrodes. These-equitietential surfaces vafry'in relative strength in. accordance with the ,potentialsto which theqyarious electrodes are charged. .Depending ppon (the angle of incidence at which the component; ions of the ion beam .encounterthe ldescribed equiand. also upon the electrical ing equal mass to charge ratios arejdivertedfrom their normal trajectories and directed to a,cornmon initial. focus in the region ,of. the ijori receiver. Further, the field. set upfbyflelectrodes i9 and'22 of the lens Hcauses a verticallioousing of the ion beam along the planesof electrodes 19 and 22,-whereby v of electrodes 20. and 23 the ,greatest .iongdensity will occur midway of the spaces between successive planar lde'cksof electrodeslllfluand fl and thereby will result ina decreased...i on.beamlabsorptionbytheclectric lens' I ,l

The important .improvementlembodiefd .'in. 1the over electric lenseslo'f Ithe t pe overlying planar'decks disposed transvcrsejosthe magnetic field, liesin thefofisetalonggtheqma netic field of the trailing electrodes .with respect ,to the leading electrodes, .wher'ebythe. overk ll ion absorption .of the. lens. is reduced by a ,decrease in the ion absorptionby..the.ltrailing;electrodes due to the offiset vpositioning defining an electrostatic lens, said groups of elecelectrodes. The leading electrodes referred to in the foregoing are those electrodes nearest the ion source, whereas the trailing electrodes are those electrodes nearest the ion receiver.

Inasmuch as the salient features of this invention have been described in detail with respect to one embodiment it will, of course, be apparent that numerous modifications may be made within the spirit and scope of this invention and it is not therefore desired to limit the inv ntion to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

,1. In an apparatus used for the electromagnetic separation of ions or isotopes including a Jtank, a magnetic field through said tank, an ion source, a divergent arcuate ion beam the plane of which lies transverse to said magnetic field, andan ion receiver; a first group of curvilinear strip electrodes planarly nested and arranged in parallel spaced planar decks with their p a a su ce no a to i ma n t fiel .a second group of curvilinear strip electrodes ,planarly nested and arranged in parallelspaccd planar decks with their planar surfaces .normal to said magnetic field, the outermost edges of said first group ,and said second group lying :symmmetricallywithin a shield shaped magnetic projection, said second group being offset along said ;magnetic field with respect to said first :group with the outer electrodes thereof being substantially -coplanar with the outer electrodes of said first group and potential .-;supply means impressing a different potential upon each of said groups orelectrodes, thereby defining equi- :potential electric lenssuriaces.

.2. In an apparatus used for the electromagnetic separation of ions or isotopesiincludinga ztank ,;having a magnetic field passing theresthrol an ionsource, a divergent arcuate ion =beam,the plane of whichlies transverse to said vmagncticfield, and. an ion receiver; a first group -..of curvilinear strip electrodes planarly nested and arranged in .parallel spaced planar decks with their planar .surfacesnormalto saidznag- .netic field, .a second group of, curvilinear strip electrodes :planarly nested and arranged in par- ;.a1-led spaced planar, decks with their planar surfaces normal to said magnetic field, the outermost edges of said first group lying symmetritca'lly within a shield shaped magnetic projection,

--the-.individual electrodes of said second :g roup being -offset,along said magnetic field with ,re- .speot to the. individual electrodes of. said :first group, ;means for charging; each of said groups Dielectrodes ,to aidifierent potential, thereby ztrodesz-lbeing symmetrically arranged with re- .spect to the radial bisectorof the ,ion be am, arc whereby ions having equalmass to charge ratios .arezdirectedtto .any initial, focu in the region of said receiver.

3.: In 1311 electric lens :ior the focusing of charged particles and disposed within a magnetic ":field, :the improvement comprising a first set ,of Jelectrodes spaced along. and normal .to said-imagneticfield andhaving central and end electrodes,

asecond set of electrodes spaced along and normal-to said'magnetic-field and having central e p t to thecent ia e ec rod 915c firsan die ec red ubstant al y sepiaa t h d ele tro e sa first. et, an po supply. ean m e s n 0te'n a n.- sa d electrodes offset along said;magnetic' field with electrodes define equipotential surfaces focusing charged particles passing therethrough.

4. In an electric lens for the focusing of charged particles the improvement comprising a magnetic field directed normal to the path of charged particles to be focused, at first group of electrodes divided into first and second rows aligned along the magnetic field, the electrodes of said first group being curvilinear and parallel, with the electrodes of the first row offset along said magnetic field with respect to the electrodes of the second row and all electrodes of said first group being at the same potential, and a second group of electrodes at a different potential than the electrodes of said first group and being divided into first and second rows aligned along said magnetic field, individual electrodes of said first and second rows being coplanar with and adjacent the individual electrodes of the first and second rows respectively of said first group, the electrodes of said second group having the same curvature as the adjacent electrodes of said first group whereby a pair of equipotential sur faces are formed between said first and second rows of electrodes and charged particles passing perpendicularly therethrough are deflected away from the electrodes thereof.

HERBERT W. B. SKINNER.

No references cited. 

